Optical system



Q'TIHTCR Jan. 3, 193 w. J. ALBERSHEIM 2,1 1 X OPTICAL SYSTEM Original Filed June 4, 1936 mam/70 W J. ALBERSHE/M ATTORNEY Patented Jan. 3, 1939 UNITED STATES PATENT OFFICE OPTICAL SYSTEM Walter J. Albersheim, New York, N. Y., assignor to Electrical Research Products, Inc., New York, N. Y., a corporation of Delaware Original application June 4,, 1936, Serial No. 83,514. Divided and this application June 9, 1937, Serial No. 147,214

3 Claims.

This application is a division of my copending application Serial No. 83,514 filed June 4, 1936.

This invention relates to an optical system and particularly to an optical system for reproducing a sound record impressed upon a photographic film The object of the invention is an optical system which when illuminated by a source oLlight of constant intensity will produce a narrfiv bandiinum/"" of light in which the intensity at,the center of the band is a maxrmma. nd dgreases uniformly outward from the center of the band.

A feature of the invention is an optical stop placed in front of the image formed by the optical system to modify the intensity of the image.

In the drawing:

Fig. 1 is a plan view of the invention embodied in a film sound reproducing system and having two sets of stops in the optical system;

Fig. 2 is an elevation of the system shown in Fig. 1;

Fig. 3 is a plan view of a reproducing system embodying the invention and having only one stop in the optical system; and

Figs. 4, 5 and 6 show alternative forms of the stop shown in Figs. 1, 2 and 3.

In Figs. 1 and 2 light from the filament l2 of a scanning lamp is focussed by the condensing lens system l3 on a film sound record M. An image of the illuminated width of the sound record I4 is formed by the lenses l5, IS in the plane of the rear scanning slit H. The rear scanning slit H may form a part of a conventional film sound reproducing system. An opaque plate ll having a rectangular aperture forms a stop for the lens l5, IS. A second opaque plate l8 pierced with an aperture, or a pair of plates, is interposed in the beam between the lenses l5, l6 and the plane of the image. The edges of the aperture in the plate I8 are located at the intersection of the-lines from the center of the image to the edges of the lens stop and from the ends of the image to the opposite edges of the lens stop. Under these conditions, the intensity of the light at the center of the image formed in the slit II will be a maximum and will decrease uniformly to zero at both ends of the slit II. This result may be checked by imagining the eye to be placed at the upper end of the slit II. The upper edge of the stop I8 will then be in line with the lower edge of the stop H and no light will reach the eye. Thus, the intensity of the image will be zero. Now, if the eye be moved a short distance nearer to the center of the image in the slit H, a small part of the illuminated portion of the If the stop i8 is moved from the position shown in the drawing nearer to the image plane in the slit l l, the upper edge of the stop l8 will prevent any light from reaching a portion of the upper part of the slit H. Thus, in this case, the intensity of the light forming the image will be a maximum for a short distance at the center of the slit l l, and will decrease uniformly to zero at a point in the upper part of the slit H and will be zero from that point to the end of the slit II.

The light forming the image will vary similarly in the lower part of the slit II.

If the stop I8 is moved nearer to the lens IS, the intensity of the light forming the image will be a maximum at the center of the slit II (but will be less in absolute magnitude than in the cases discussed hereinabove) and will decrease uniformly to the ends of the slit H, but will not 7 decrease to zero at the ends.

In Figs. 1, 2 and 3 similarly numbered elements have similar functions. In Fig. 3 the single unstopped lens l5 replaces the stop lens system l5, l6, II of Figs. 1 and 2. In the case shown in Fig. 3, the line defining the location of the aperture in the plate I8 runs from the center and ends of the image formed in the slit H to the two edges of the lens l5.

As described in connection with Figs. 1 and 2, the interposition of the stop l8 will cause the intensity of illumination of the image formed in the plane of the slit II to vary from a maximum at the center of the slit to a minimum at each end.

It is not essential that the intensity of the image formed in the plane of the rear scanning slit II should vary uniformly outward from the center of the slit. The intensity of the image at two points equidistant from the center should be equal, thus producing a condition which may be termed reverse symmetry. And, considering only one-half of the image, the intensities of the image at any two points equidistant from the center line of the half image (the quarter lines of the whole image) should together equal a constant, thus producing a condition which may be termed inverse symmetry.

The stop ll may be formed or two parallel plates or of a rectangular aperture in a single plate, as shown in Fig. 6. The aperture may also be formed as shown in Figs. 4 and 5, in which the radii of all the curves are one-half of the distance between the intersections of the line shown in Figs. 1 and 3. While the invention has been shown as embodied in a film sound reproducing system using a rear scanning slit, it will be evident that many variations may be made within the scope of the invention. For example, the stop l8 may be located between the lens l3 and the image of the filament formed on the film l4 and thus cause the intensity of the light impressed on the film H to vary in a manner similar to the variation in the intensity of the light forming the image in the plane of the rear scanning slit ll.

What is claimed is:

1. In an optical system, an illuminated object, a lens system for forming an image of said object, and means comprising an optical stop to cause the intensity of said image to vary in reverse symmetry Irom the center to both ends and rut-h 5 to cause the intensity of each half 01' said image to vary in inverse symmetry with respect to the intensity of the center oi? the half image.

2. In an optical system, a uniformly illuminated obiect, a lens system for forming an image oi said obJ'ct, and means comprising an optical stop located between the lens and the image plane to cause the intensity of said image to vary in reverse symmetry from the center to both ends of said image and to cause the intensity of each half of said image to vary in inverse symmetry with respect to the intensity of the center of the half image.

3. In an optical system, a uniformly illuminated rectangular object, a lens system for forming an image of said object, and means comprising an optical stop located between said lens and the image plane to cause the intensity of said image in one direction to be substantially constant and to cause the intensity of said image in a direction normal to said first direction to vary symmetrically from the center to both ends of said image.

WALTER J. ALBERSHEIM.

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